Retrieving an entity instead of persisting it during a request - symfony

Question

I'm using api-platform and I have a Book entity that has a ManyToOne relation to a Writer.
All writers are already persisted in the database, so I'd like to be able to create Books with a POST request containing the writer it is bound to.
But it keeps trying to persist a new writer.
How can I achieve that ?
Edit:
Books
/**
*
* #ORM\Entity(repositoryClass="App\Repository\BooksRepository")
* #ApiResource(
* attributes={
* "normalization_context"={"groups"={"read"}}
* }
*
* )
*/
class Books
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\ManyToOne(targetEntity="App\Entity\Property", inversedBy="beans")
* #ORM\JoinColumn(nullable=false)
* #Groups({"read"})
*/
private $property;
public function getProperty(): ?Property
{
return $this->property;
}
public function setProperty(?Property $property): self
{
$this->property = $property;
return $this;
}
}
Writers (also called Property)
/**
* #ORM\Entity(repositoryClass="App\Repository\PropertyRepository")
*/
class Property
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
* #Groups({"read"})
*/
private $id;
/**
* #ORM\Column(type="string", length=30)
* #Groups({"read"})
*/
private $type;
/**
* #ORM\OneToMany(targetEntity="App\Entity\Books", mappedBy="property", orphanRemoval=true)
* #Groups({"read"})
*/
private $books;
public function __construct()
{
$this->books = new ArrayCollection();
}
public function getId()
{
return $this->id;
}
public function getType(): ?string
{
return $this->type;
}
public function setType(string $type): self
{
$this->type = $type;
return $this;
}
/**
* #return Collection|Books[]
*/
public function getBooks(): Collection
{
return $this->books;
}
public function addBook(Books $book): self
{
if (!$this->books->contains($book)) {
$this->books[] = $book;
$book->setProperty($this);
}
return $this;
}
public function removeBook(Books $book): self
{
if ($this->books->contains($book)) {
$this->books->removeElement($book);
// set the owning side to null (unless already changed)
if ($book->getProperty() === $this) {
$book->setProperty(null);
}
}
return $this;
}
}

Answer 1

The following request should do the trick:
POST /books
{
"property": "/writers/1"
}